Infusion apparatus

ABSTRACT

In an infusion apparatus, an infusion line ( 4 ) connects a container ( 2 ) of an infusion fluid to an extracorporeal blood circuit ( 23 ). A first valve ( 6 ) closes the infusion line downstream of an infusion pump ( 5 ). An expansion chamber ( 9 ), provided with a pressure sensor ( 10 ), is arranged between the infusion pump and the first valve. A second valve ( 8 ) closes a vent line ( 7 ) of the expansion chamber. The processor closes the first valve when the container is emptied. After replacement with a new and full container, the processor restarts the pump and selectively opens the first valve or the second valve according to the increase in pressure measured in the expansion chamber.

BACKGROUND OF THE INVENTION

The invention relates to an infusion apparatus and to a control methodfor an infusion apparatus.

Specifically, though not exclusively, the invention can be usefullyapplied for infusion of a medical fluid to a patient, either directlyinto the patient's body, for example into his or her vascular system, orvia an extracorporeal blood circuit connected to the patient.

WO 87/05225 teaches an infusion system comprising a drip chamber havinga pointed upper inlet end for insertion of a container of an infusionfluid. The chamber is provided with an inlet valve and an outlet valvecontrolled by a control unit. The top of the chamber is connected to apiston gas compressor via an auxiliary line provided with a pressuresensor. The control of the infusion flow rate is done as follows. Withboth the valves closed and an initial pressure P₁ in the chamber, thepiston is displaced forward such as to reduce the volume by apredetermined quantity ΔV. According to Boyle's law, this reduction involume corresponds to a proportional increase in gas pressure ΔP. Atthis point the outlet valve is opened to dispense the infusion fluid.When the pressure has dropped by a quantity ΔP, which means that aninfusion fluid volume of ΔV has been dispensed, the outlet valve isclosed. After this the piston returns back to its initial position, theinlet valve is opened so the chamber can be filled to initial pressureP₁, and a new cycle commences.

EP 1319417 illustrates a disposable infusion system for injecting aninfusion fluid into the body of a patient. The infusion system comprisesa fluid conduit situated between a source of an infusion fluid and thepatient, a peristaltic pump operating on the fluid conduit, a gas-liquidseparation chamber downstream of the pump, a pressure sensor in thechamber, and a clamp for blocking the fluid conduit downstream of thechamber. The pressure sensor is arranged on a service line whichbranches from the top of the chamber and which is provided with ahydrophobic-membrane protection device for protecting the pressuresensor against contamination by the liquid in the chamber. If the liquidreaches the membrane the membrane becomes gas-sealed and is no longerable to transmit the pressure to the sensor. In these conditions themeasured pressure does not correspond to the real pressure in thechamber. A monitoring unit determines the quantity of gas in the systemso as to detect, over time, a situation of risk of the liquid reachingthe membrane. The monitoring unit measures the initial pressure P₁, andthen injects into or extracts from the system a predetermined fluidvolume ΔV, after which it newly measures the pressure P₂, and calculatesthe gas volume in the system as a function of P₂, P₁ and ΔV.

EP 1319417 teaches a further monitoring method of a disposable fluidconduit system connected to a medical apparatus, in particular with theaim of testing the integrity of the system (for example the absence ofleaks) and of checking that the installed disposable system is theappropriate one for the desired treatment. The monitoring methodincludes continuously measuring the pressure in the system, injecting orextracting a volume of fluid ΔV into or from the system until apredetermined pressure P₂ is reached in the system, and finallydetermining the state of the system from a comparison between ΔV and astandard predetermined value.

SUMMARY OF THE INVENTION

An aim of the present invention is to provide a fluid infusion liquid inwhich the risk of infusion of gaseous parts (air) present in the liquiditself is reduced.

A further aim of the invention is to realise a control method forreducing the above-mentioned risk.

An advantage of the invention is to provide an infusion apparatus whichcan reduce the need for intervention on the part of an operator, withthe aim of reducing the risk of the presence of gaseous parts (air) inthe infusion liquid. In particular the invention enables a reduction orelimination of the interventions required by the operator in order toeliminate excesses of air in the infusion circuit.

A further advantage is automatically to eliminate excess air in theinfusion circuit, in particular each time a used container of theinfusion fluid is replaced with a new and full container. The excess aircan advantageously be eliminated during a first infusion circuit primingstage, or in a first filling stage of the infusion circuit with a liquidwhich expels air from the circuit at the same time.

A further advantage is to make available an infusion apparatus which isconstructionally simple and economical and which is also very reliable.

These aims and others besides are all attained by the invention as it ischaracterised in one or more of the accompanying claims.

In a specific embodiment of the invention, the infusion apparatus maycomprise a batch container of an infusion fluid, an infusion lineconnected to the batch container, an infusion pump operating on theinfusion line, an infusion block valve arranged downstream of theinfusion pump, and a vent valve arranged between the infusion pump andthe block valve. In a specific embodiment of the invention, the infusionapparatus may comprise a gas-liquid separator (for example a separationor expansion chamber) arranged between the infusion pump and the blockvalve, and a sensor designed to provide a signal indicating the quantityof liquid and/or gas in the gas-liquid separator. The sensor maycomprise, for example, a pressure sensor for providing a signal of theliquid level in the separator, or a float device for providing a signalwhen a predetermined liquid has reached a predetermined level in theseparator, and so on.

In a specific embodiment of the invention, the infusion apparatus maycomprise an infusion line, a pump operating on the infusion line, aninfusion block valve arranged downstream of the pump, a vent valvearranged between the pump and the block valve, a pressure sensorarranged between the pump and the block valve, and a processorprogrammed to perform the operations of: closing both the valves in atleast a particular situation, for example when the infusion fluidcontainer is to be changed; activating the pump with both valves closed;and selectively re-opening one or the other of the valves according tothe pressure signal provided by the pressure sensor.

In a specific embodiment of the invention, the processor may beprogrammed to selectively re-open one or the other valve according to avalue indicating the ratio between the pressure change measured by thepressure sensor and the volume of fluid pumped by the pump during theabove-cited measured pressure change.

In a specific embodiment of the invention, the processor may beprogrammed to stop the pump when the pressure measured by the pressuresensor exceeds or reaches a predetermined threshold level.

Further characteristics and advantages of the present invention willbetter emerge from the detailed description that follows of someembodiments of the invention, illustrated by way of non-limiting examplein the accompanying figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be made herein below with reference to theaccompanying figures of the drawings, which are provided by way ofnon-limiting example.

FIG. 1 illustrates a first embodiment of the infusion apparatus madeaccording to the invention.

FIG. 2 is a second infusion apparatus made according to the invention.

FIG. 3 is a third infusion apparatus made according to the invention.

FIG. 4 is a fourth infusion apparatus made according to the invention.

DETAILED DESCRIPTION

With reference to FIG. 1, 1 denotes in its entirety an infusionapparatus for infusing a fluid, in particular a medical fluid, into ahuman being. The infusion apparatus 1 can be used for infusing a medicalfluid into the vascular system of a patient. This infusion can occurdirectly, i.e. by means of a direct connection with a vascular accessdevice, or by means of an extracorporeal blood circuit 23, such as forexample a usual blood circuit of a dialysis set. The infusion fluid(medical fluid) can comprise a replacement fluid used in ahemo(dia)filtration treatment. In particular it can comprise areplacement fluid used in an AFB treatment (“acetate freebiofiltration”). The medical fluid can however comprise any known typeof infusion fluid which can be introduced into a human body.

The infusion apparatus 1 comprises a container 2 having a limitedcapacity and containing the infusion fluid. The container 2 is a batchcontainer. In other words the container 2 may be configured for discreteand not continuous functioning, i.e. it may be filled before use with adetermined quantity of infusion fluid and be emptied during use whilesupplying the infusion fluid to a user. In substance the infusion systemdescribed herein may refer to infusion of a medical fluid in which themedical fluid is sourced from a batch-type source, i.e. a supply systemin which the infusion fluid is prepared in one or more batches indiscrete quantities which, during use, empty and which can be replacedtime-by-time as they are emptied.

The container 2 can comprise one or more bags having flexible walls. Thecontainer 2, of known type, is provided with one or more access portseach provided with a sealing device of known type, for example abreakable membrane and/or a removable cap, or another type.

The batch container 2 of the infusion fluid is connected to a weightsensor 3 designed to emit a weight signal in relation to the weight ofthe container. The weight sensor 3 can comprise any type of scales ofknown type.

The infusion apparatus 1 further comprises an infusion line 4 having afirst end which is connected to the container 2 in order to receive theinfusion fluid, and a second end for supplying the infusion fluid to theuser (for example the extracorporeal blood circuit 23). The infusionline 4 can comprise any type of infusion line of known type. The firstend of the line 4 is connected to the container 2 by means of aknown-type connection, for example by means of a removable connection(as illustrated and denoted by 13 in FIGS. 3 and 4), such as inparticular a luer connector, or a piercing nozzle-type connection (thenozzle being associated to the first end of the line 4) which penetratesinto a perforable or breakable closure predisposed on the access port ofthe container 2. It is however possible to use any type of knownconnection between an infusion line and an infusion fluid container. Aremovable-type connector enables simple and rapid changing of thecontainer 2 when empty for a new and full container 2, while maintainingthe operativity of the other elements of the infusion apparatus.

The infusion apparatus 1 further comprises an infusion pump 5 operatingon the infusion line 4 for circulating the infusion fluid from the firstend to the second end of the line itself. The infusion pump 5 may be anocclusive-type pump, i.e. a pump which in a non-activated condition, orwhen stationary, occludes the infusion line 4. The infusion pump 5 maybe a positive-displacement pump. The infusion pump 5 can comprise, forexample, a tube-deforming pump (peristaltic). In the specific embodimentthe pump is rotary. The infusion line 4 comprises a pump tract designedfor coupling with the infusion pump 5. In the specific embodiment thepump tract comprises a segment of tube which is open-ring-shaped (forexample a U shape) which engages with a roller rotor belonging to therotary peristaltic pump. It is, however, possible to use other knowntypes of pumps (in particular positive displacement pumps) forcirculating the fluid in a fluid transport line, in particular of thetypes used in medical lines.

The infusion apparatus 1 comprises a first valve 6, or a check valve ofthe infusion fluid, designed to close the infusion line 4 between theinfusion pump 5 and the second end of the infusion fluid supply line.The first valve 6 comprises, in the specific case, a valve commanded bythe control unit of the infusion apparatus 1. A manual valve, operatedby the operator, could be used. The first valve 6 can comprise a mobileobturator organ which operates by squeezing a tract of tube of theinfusion line 4. This tract of tube has elastic return properties, suchas to return into the open configuration allowing fluid passage onreopening of the valve. The first valve 6 comprises, in the embodiment,a tube-blocking clamp of known type, e.g. electromagnetically activated.

The infusion apparatus 1 further comprises a vent line 7 having a firstend which is connected to an intermediate tract of the infusion line 4and a second discharge end. This intermediate tract of the infusion line4 is arranged between the infusion pump 5 and the first valve 6. Thevent line 7 comprises, in the specific case, a length of flexible tubeused for fluid transport in the medical area. The vent line 7 serves, inparticular, to expel excess gas from the intermediate tract of theinfusion line 4, as will be better explained herein below.

The vent line 7 is provided with a second valve 8, or a vent valve inthe intermediate tract of the infusion line, designed to close the line7 itself. The second valve 8 comprises, in the specific case, a valvecommanded by the control unit of the infusion apparatus. A manual valveactivated by the operator could also be used. The second valve 8 cancomprise a mobile obturator which operates by squeezing a tract of tubeof the vent line 7. The tract of tube has elastic return properties, soas to return into the open configuration, allowing fluid passage, onreopening the valve. The second valve 8 comprises, in the example, atube blocking clamp of known type, e.g. electromagnetically activated.

The infusion apparatus 1 comprises an expansion chamber 9 arranged inthe intermediate tract of the infusion line. The expansion chamber 9 isin effect an enlargement of the fluid passage section of the infusionline 4. The expansion chamber 9 produces a slowing down of the infusionfluid flow along the infusion line 4. The expansion chamber 9 may have atransversal section having a greater surface than the transversalsection of the two tracts of tube which are part of the infusion line 4and which are constituted by an inlet tract of the chamber 9 (on whichthe pump 5 operates) and by an outlet tract from the chamber 9 (on whichthe first valve 6 operates). The tract of inlet infusion line in theexpansion chamber may be connected to the container 2 of the infusionfluid, while the tract of outlet infusion line from the expansionchamber is connected to the user (blood circuit). The infusion line 4may exhibit an inlet into the expansion chamber 9 and an outlet from theexpansion chamber 9, in which the inlet is located at a higher positionthan the outlet. The expansion chamber 9 functions as a gas/liquidseparator. The expansion chamber 9 may be destined to contain adetermined quantity of infusion fluid such as to maintain a liquid leveldelimiting an upper part of the chamber which is full of air.

The infusion apparatus 1 can further comprise a first pressure sensor 10for emitting a first signal indicating the pressure in theabove-mentioned intermediate tract of infusion line 4. In the specificcase the first pressure sensor 10 is operatively associated to theexpansion chamber 9. In particular the first pressure sensor 10 may bean elastically-deformable membrane sensor having an internal side whichfaces towards the inside of the expansion chamber 9 and an external sidewhich communicates with a pressure transducer (of known type and notillustrated) connected to the control unit of the infusion apparatus 1.The pressure transducer may be predisposed such as to be able to measurethe pressure in the inside of the expansion chamber 9. The firstelastically-deformable membrane sensor 10 may be solidly associated tothe body of the expansion chamber 9. In particular, the membrane canhave the edge thereof tightly engaged between two half-shells which arepart of the body of the expansion chamber 9. It is possible to use othertypes of known pressure sensors, such as for example the pressuresensors already used in the medical field for measuring the pressure inextracorporeal blood circuits. In particular it is possible to use apressure sensor comprising a service line connecting the expansionchamber 9 with a pressure transducer—in turn connected to the controlunit of the infusion apparatus—via the interpositioning of atransducer-protector device having a hydrophobic membrane (also known asa blood catcher).

In the specific example the first end of the vent line 7 is connectedwith an access port arranged at the top of the expansion chamber 9. Thevent line 7 may open into the upper part of the expansion chamber 9which, in use, may be occupied by a volume of gas (air) which overliesthe liquid level in the lower part. The second end of the vent line 7may be connected, as in the specific example, with the part of theinfusion line 4 located upstream of infusion pump 5, so as to form aring. In particular the vent line 7 may have the second end engaged(fixed or removably) in an access port arranged on the infusion fluidcontainer wall 2. In other embodiments the second end of the vent linecan be connected to an element chosen from a group of elementscomprising, apart from the container 2 of the infusion fluid: an initialtract of the infusion line 4 comprised between the container 2 and thepump 5, a hydrophobic filter connected to the atmosphere, an aspiratingdevice, a fluid transport line connected to a fluid chamber of a bloodtreatment device having a semipermeable membrane which separates thefluid chamber from a blood chamber, and a used fluid discharge line of ahemo(dia)filtration apparatus. In FIGS. 2 to 4, some examples of thesedifferent embodiments are illustrated.

The control unit (processor) of the infusion apparatus 1 is connected tothe first pressure sensor 10 in order to receive the pressure signal ofthe internal pressure in the expansion chamber 9. The control unit maybe further connected to the weight sensor 3 in order to receive theweight signal of the container 2 of the infusion fluid. The control unitmay be designed to control the infusion pump 5, the first valve 6(infusion fluid check valve) and the second valve 8 (vent valve of theintermediate tract of the infusion line 4).

During the normal process of infusion the control unit controls theinfusion pump 5 according to the weight signal received from the weightsensor 3, with the aim of providing a predetermined flow rate of theinfusion pump 5 in order to obtain the desired dose of infusion fluid.During the normal infusion process the control unit maintains the firstvalve 6 open and the second valve 8 closed. The control unit furthermonitors the pressure in the expansion chamber 9 in order to detect anyfaults in the infusion process—faults which are recognised if, forexample, the pressure in the expansion chamber 9 no longer falls withinone or more predetermined safety ranges—and in order to interveneautomatically such as to place the infusion apparatus in safetyconditions vis-a-vis the patient. The faults which might occur are, forexample, possibly a blockage or obstruction in the infusion line 4, of aleakage of liquid in the line itself, or a malfunctioning of theinfusion pump 5, and others besides.

The control unit of the infusion apparatus may be programmed toautomatically perform a procedure of recognition that the container 2 ofthe infusion fluid has emptied, and a procedure for restarting theinfusion process after replacement of the empty container 2 with a fullone.

As mentioned herein above, the control unit is programmed to perform thenormal infusion procedure, in which the first valve 6 is opened and keptopen in order to allow the infusion fluid to flow towards the user(blood circuit), while the infusion pump 5 is activated with the firstvalve 6 open in order to supply the desired flow rate under the controlaccording to the weight signal supplied by the weight sensor 3. Insubstance, the control unit acquires at least a weight value for thecontainer 3 (for example it can acquire a series of values according toone or more predetermined measuring frequencies), compares the weightvalue detected against a reference value, and on the basis of thiscomparison controls the infusion pump flow rate. The reference value canbe, for example, the value of the weight measured in the preceding step,or a series of weight values measured during the previous steps. Thecontrol of the normal infusion weight is however substantially of knowntype and can be performed in any of the systems in the prior art (forexample by a usual PID retro-active control). The recognition procedurefor detecting an empty infusion fluid container is also substantially ofknown type and can comprise any one of the known systems for recognisingthe emptying of a container (end bag). This procedure can comprise, forexample, a stage of comparing a weight value detected (for example, thelast one) with a reference value which can be constituted, for example,by a previously-acquired weight value of the container (for example thepenultimate one) with the aim of assessing whether the weight of thecontainer is no longer dropping. In substance the control unit may notethat the container 2 is empty because its weight no longer drops over acertain period of time. Another system can compare against a referencevalue constituted by a predefined value indicating the weight of thecontainer 2 when empty of fluid. In this case the weight of thecontainer can be known before. If the control unit recognises that thecontainer 2 is empty, it intervenes to put the system into safety mode;this intervention can comprise, for example, one or more of thefollowing actions: signalling a faulty situation (for example byemitting a sound or a visual signal via the user interface connected tothe control unit) and/or stopping the infusion pump 5 and/or closing thefirst valve 6. These procedures, as is known, have the drawback ofalmost inevitably causing ingress of air into the infusion line 4. Thisair can be separated in the expansion chamber 9, giving rise however toa lowering of the liquid level in the chamber itself. If the level getstoo low there is the risk that, on restarting the infusion process afterhaving replaced the empty container 2 with a new full container 2, theremight be air which can be directed towards the zone of use (bloodcircuit), with grave risks to the health of the patient.

To obviate this drawback, the control unit of the infusion apparatus maybe programmed to perform the following control procedure of the infusionon restarting the infusion process, after changing the empty container 2with a full container 2 of the infusion fluid. This control procedurecan be activated by the operator who, after having replaced thecontainer 2, gives the control unit the instruction or series ofinstructions for initiating the control procedure. This instruction cancomprise, for example, a command (such as a button or a touch-button ofa touch-screen) given on the user interface of the infusion apparatus.The control procedure may comprise a stage of acquiring the pressuresignal in the expansion chamber 9 (i.e. in the intermediate tract of theinfusion line 4 comprised between the infusion pump 5 and the firstvalve 6) and a stage of selectively commanding the opening of either thefirst valve 6 or the second valve 8 on the basis of the pressure valuemeasured. In particular acquiring the pressure value (or series ofpressure values) in the expansion chamber 9 may be done after havingactivated the infusion pump 5. This activating of the pump 5 willproduce a flow in the direction going from the infusion container 2 tothe expansion chamber 9. Since both the first valve 6 and the secondvalve 8 are closed, in this configuration the intermediate tract of theinfusion line 4—which comprises the expansion chamber 9—forms a closedsystem. Thus the flow of a certain quantity of fluid into theintermediate tract will determine a certain pressure increase, which canbe measured by the pressure sensor 10. If this pressure increase isrelatively high, it means that the fluid which has entered theintermediate tract moved by the positive-displacement pump 5 contains arelatively high percentage of liquid part with respect to gaseous part.If, on the other hand, this pressure increase is relatively small, itmeans that the fluid moved into the intermediate tract of the pump 5contains a relatively high percentage of gas with respect to liquid. Inother words, the pressure change in the intermediate tract, assessed inrelation to the volume of fluid which the positive-displacement pump 5pushes into the intermediate tract, provides an indicator of thequantity of gas (air) introduced into the intermediate tract. Thecontrol unit may be therefore programmed to stop the pump 5 when thepressure in the intermediate tract exceeds a predetermined thresholdlevel. This threshold level can be, for example, predetermined accordingto the desirable working pressure required in the expansion chamber 9during the normal infusion process. This working pressure is correlatedin a known way to the volume of the expansion chamber 9, to the level ofliquid in the chamber 9 and to the desired quantity of air required inthe chamber during the normal infusion process. The quantity of air inthe chamber will depend on the working pressure and the desired level ofliquid, once the volume of the expansion chamber 9 is fixed and known(which is in the present example is not variable). Let us suppose thatthe above-cited threshold value is made to coincide with the workingpressure value or with a value close thereto. In this case, the controlunit may be programmed to stop the pump 5 on reaching the cited pressureand to decide, at this point, whether to open the second valve 8 (ventvalve) or the first valve 6 (infusion blocking valve) on the basis of acriterion depending on the volume pumped by the pump 5 in theintermediate tract in order to reach the predefined pressure. Inparticular, the second valve 8 may be opened if the pumped volume isrelatively high (for example above a prefixed threshold value), becausethis means, as previously mentioned, that in the volume of fluid pumped(which has entered the intermediate tract) there is a high quantity ofgas with respect to the liquid. The opening of the second valve 8 willthus produce removal of part of the air contained in the intermediatetract. The second end of the vent line 7 (i.e. the end beyond the ventvalve 8) is in communication with an environment kept at a pressurewhich is below the pressure reached in the expansion chamber 9. In otherwords, the opening of the vent valve 8 will produce a reduction in thepressure in the expansion chamber 9 (intermediate tract of the infusionline) such as to reach a situation of equilibrium with the environmentin which the vent line 7 terminates. At this point the vent valve(second valve 8) is closed and a new cycle of activating the infusionpump 5 may begin, up until it newly reaches the threshold pressure inthe intermediate tract. As long as the pumped volume in each pumpingcycle is relatively high, the cycle (i.e. in which the control unitopens the second valve 8—vent valve—to enable expulsion of the excessair and thus the lowering of the pressure) is repeated. If on the otherhand the pumped volume is relatively small (for example less than apredetermined threshold value), the first valve 6 may be opened(infusion blocking valve) and the normal infusion process canrecommence, as this means, as previously mentioned, that there is asmall or almost negligible amount of gas in the volume of pumped fluid(which has entered the intermediate tract). In the latter case, insubstance, it is taken that there is no longer any air internally of theinfusion line 4 upstream of the chamber itself and that the liquid levelin the chamber 9 is the desired level; thus the normal infusion processcan be restarted without any danger of an undesired ingress of air andwithout the liquid level in the chamber lowering any further.

The control unit for the infusion apparatus, as has been described, maybe therefore programmed to close the first valve 6 and the second valve8, to activate the pump 5 and to command a selective opening of thefirst valve 6 or the second valve 8 on the basis of the pressure signalreceived. In particular, the control unit may compare the pressure valuereceived with a reference value (predefined and stored in the controlunit's memory), and open the second valve 8 following the comparison.During the pump 5 activation stage, the control unit may be programmedto close the first valve 6 and to leave it closed at least during theabove-described pump 5 activation stage 5, so that the intermediatetract of the infusion line (where the expansion chamber 9 is located)forms a closed system.

The control unit may be programmed to perform a sequence of stages whichcomprises: closing the first valve 6 and the second valve 8, activatingthe pump 5, determining at least a value of pressure change in theintermediate tract during a predetermined variation of another parameterwhile the pump 5 is in the activation stage, comparing theabove-mentioned pressure variation value with a reference value, andopening the first valve 6 or the second valve 8 according to thecomparison. During this sequence of stages the first valve 6 and thesecond valve 8 may be both closed. The above-mentioned other parameteris, in the specific case, the volume of fluid pumped by the infusionpump 5, or a parameter indicating this volume (such as for example thenumber of revolutions of the rotary positive displacement infusionpump). The above-mentioned other parameter can be selected from thegroup of parameters comprising, apart from the volume of pumped fluid,the time, the displacement of a mobile element of the infusion pump 5,the weight of the container 2 of the infusion fluid.

The control unit may be programmed to perform the following sequence ofstages: closing the first valve 6, closing the second valve 8,activating the pump 5 with the first valve 6 closed and the second valve8 closed, acquiring at least a pressure value in the intermediate tract(for example while the pump 5 is in the stage of activation or after ithas been functioning for a certain period of time), acquiring at least avalue of the pressure change in the intermediate tract (for examplewhile the pump 5 is in the stage of activation or after it has beenfunctioning for a certain period of time), opening the second valve 8when the pressure value exceeds a threshold value, re-closing the secondvalve 8 and repeating the above-mentioned stages up until the pressurechange value has reached a threshold value. In substance, the pumpingcycle may be interrupted and then recommences with the normal infusionprocess (opening the first valve 6) when the derivative of the pressureas a function of another parameter (where by derivative we mean thepressure change measured on varying the other parameter, which can be,for example, the time or fluid volume pumped or the weight of the fluidpumped) is sufficiently high.

In a further embodiment (see FIG. 2, in which the same elements as thosein FIG. 1 have been denoted using the same numbers) the infusionapparatus further comprises a second pressure sensor 11 for emitting asecond signal indicating the pressure in an initial tract of infusionline 4 comprised between the container 2 and the pump 5. The secondpressure sensor 11 can comprise any known pressure sensor used in afluid circuit for medical use. In the case of FIG. 2 the control unitmay be programmed to perform the following sequence of stages: acquiringat least a pressure value in the initial tract supplied by the secondpressure sensor 11, comparing the above-cited pressure value in theinitial tract with a reference value, and signalling a faulty situationand/or stopping the pump 5 and/or closing the first valve 6 according tothe result of the comparison. A reduction of pressure to below athreshold value and/or a rapidity in the reduction of pressure goingbeyond a certain threshold are seen as indicating the fact that thecontainer has been emptied of infusion fluid and that therefore theoutflow from the container essentially contains air. This may serve tostop the infusion pump in order to interrupt and prevent the flow of airtowards the expansion chamber 9. In substance, the second pressuresensor 11 may be used to reduce the risk of undesired ingress of airinto the intermediate tract of infusion line 4 arranged downstream ofthe pump 5, i.e. to prevent inflow of air into the expansion chamber 9and thus the lowering of the liquid level in the chamber itself. In FIG.2, the number 12 schematically denotes the environment into which theexcess gas (air) is discharged into the expansion chamber 9 through thesecond vent valve 8. The environment can comprise one of those alreadymentioned herein above. An embodiment can be realised in which theweight sensor 3 is not present. In this case the function of signallingthe emptying of the batch container 2 can be performed by the pressuresensor (as seen herein above).

A further embodiment is illustrated in FIG. 3, where the same elementsas in FIGS. 1 and 2 have been denoted using the same numbers. The ventline 7 may be joined, at the second end in order to discharge the excessgas, to an initial tract of the infusion line 4 comprised between thecontainer 2 outlet and the infusion pump 5. The second end of the ventline 7 may be, as in the specific case, connected to the infusion line 4at an engagement point arranged between a removable connection 13 andthe infusion pump 5. The engagement between the vent line 7 and theinfusion line 4 can be either fixed and/or permanent, as in the specificembodiment, or can be removable. The removable connection 13 may bepredisposed to connect an end of the infusion line 4 with the containeroutlet 2. The container outlet 2 may be arranged on the bottom of thecontainer, with reference to a use configuration. The removableconnection 13 can be a luer-type connection, or any other removableconnection of known type.

A further embodiment is illustrated in FIG. 4, where the same elementsas in FIGS. 1, 2 and 3 are denoted using the same numbers. The vent line7 may be joined, at the second end for discharge of the excess gas, to afluid transport line which is part of an apparatus for extracorporealblood treatment. In the specific case of FIG. 4, the apparatus comprisesa membrane device 14 for extracorporeal blood treatment. The membranedevice 14 comprises, for example, a hemodialyser, or a hemo(dia)filter,or another type of membrane exchanger of known type for performing ahemoperfusion treatment, or a pure ultra filtration, or a therapeuticplasma exchange, or a congestive heart failure treatment, or hepaticfunction substitution, and so on. The blood chamber of the membranedevice 14 may be connected to an extracorporeal blood circuit having awithdrawal or removal line 15 for removing blood to be treated sourcingfrom a vascular access of the patient, a return line 16 for returningthe treated blood the vascular system of the patient, a blood pump 17for moving the blood along the extracorporeal circuit. The withdrawalline 15 and the return line 16 are connected respectively to an inletand an outlet of the blood chamber of the membrane device 14. The fluidchamber of the membrane device 14 is connected to a hydraulic circuitwhich may comprise a source 18 of a fresh treatment fluid (for examplean on-line preparation device of a dialysis fluid, or any other knowntype of a dialysis fluid source or a replacement fluid of a convectivereplacement therapy of the renal function, or any other known type ofsource of a medical fluid for replacement therapy of the hepaticfunction), a supply line 19 of the fresh treatment fluid which connectsthe source 18 with an inlet of the fluid chamber of the membrane device14, a drainage 20, and a discharge line 21 of the used treatment fluidwhich connects and outlet of the fluid chamber of the membrane treatmentdeice 14 with the drainage 20. The extracorporeal treatment apparatus isillustrated schematically in FIG. 4: it can however be constituted byany apparatus for hemodialysis or hemo(dia)filtration of known type. Inthe specific example the second end of the vent line 7 is connected tothe discharge line 21, for example by means of a fluid-sealed removableconnection 22 (a luer connection or another type of removable connectionof known type).

A further embodiment could be realised, comprising a similar apparatusto that of FIG. 4, provided with an infusion device which is configuredfor providing an infusion line in post-dilution (downstream of themembrane device 14), the pre-dilution line being predisposed in additionto or alternatively to the predilution line of FIG. 4.

The functioning of the infusion systems illustrated in FIGS. from 2 to 4is the same as that of FIG. 1.

The process for obtaining the desired liquid level as described abovecan be applied not only to the case of a change of batch container ofthe infusion fluid, but also during the infusion circuit primingprocedure, i.e. during a first filling stage of the infusion circuitwith a liquid which contemporaneously expels the air from the circuit.

The method for controlling the infusion apparatus as described above, ashas been seen, can be based on the analysis of the pressure (or anothersignal indicating the quantity of liquid and/or air, such as for examplea liquid level signal) in the tract of the infusion line arrangeddownstream of the infusion pump (positive displacement and occlusive).The control method can comprise, as mentioned, an initial stage ofclosing the first valve (the block or check valve of the infusion flowto the user) when the container has been emptied. The detection of theemptying of the container is performed, for example, by means ofmonitoring the weight of the container and/or the pressure upstream ofthe infusion pump. After the first valve has been closed the emptycontainer is replaced with a full container; this operation canactivate, for example with a command (pressing a button) on the userinterface of the infusion apparatus, the automatic procedure forevacuating any air from the infusion line before resetting the normalinfusion flow to the user. The automatic procedure can be performed invarious ways. In a first way, the pump may be activated (with the twovalves, the vent valve and the block valve both closed) up until apredetermined pressure (or liquid level) is reached downstream of thepump; if the volume of fluid pumped by the pump to reach the pressure(or liquid level) is above a threshold value, the vent arrangeddownstream of the pump may be opened in order to evacuate the excess airand thus lower the pressure downstream of the pump, after which the ventmay be closed and the operative cycle repeated, so that the pump isactivated up until it newly reaches the above-mentioned predeterminedpressure (or liquid level) downstream of the pump; this cycle may berepeated until the volume of fluid pumped by the pump in order to reachthe predetermined limit pressure (or liquid level) is lower than thethreshold value; in this case, instead of opening the vent thecommunication with the user is opened (i.e. the first valve, or checkvalve of the infusion flow is opened) and the normal infusion procedurecan recommence with the guarantee that all the excess air has beenevacuated through the vent. In a second way, the pump is activated (withboth valves closed), while the pressure increase (or the liquid level)is monitored downstream of the pump in relation to the volume of fluiddisplaced by the pump (this volume can be determined, for example, onthe basis of the pump displacement, and in the specific case, in whichthe pump is rotary, on the basis of the number of revolutions made bythe pump itself, or also, for example, on the basis of the weightmeasured by the weight sensor 3): if this ratio exceeds a certainthreshold value, it means that in the fluid downstream of the pump thereis a small quantity of gas in relation to liquid, so the normal infusionprocedure can safely be restarted; on the other hand, if theabove-mentioned ratio is lower than the threshold value after thepressure (or liquid level) downstream of the pump has reached apredetermined threshold value, the vent will be opened and the sameoperative cycle will be repeated. In a third way, the pump is activated(with both valves closed) up until it moves a predetermined volume offluid, after which the pressure increase (or liquid level) is calculateddownstream of the pump by effect of the displacement of theabove-mentioned volume; if the increase in pressure (or liquid level)exceeds a certain threshold value, it means that the liquid part of thefluid downstream of the pump is relatively high in relation to the gaspart, so that the infusion procedure can recommence in conditions ofsafety (therefore the block valve of the infusion flow is opened and theinfusion fluid is pumped normally to the user); if the pressure increase(or liquid level) is lower than the above-mentioned threshold value, itmeans that downstream of the pump the gaseous part of the fluid presentis relatively high in comparison with the liquid level, and the ventwill therefore be opened to evacuate the excess gas before being newlyclosed, the operating cycle then being repeated. Other ways might beenvisaged for performing the automatic degassing procedure, based on themonitoring of the pressure (or liquid level) downstream of he pump withone or another or both the two valves, the vent valve and the infusionblock valve, in the closed position.

In a further way, an appropriate liquid level can be re-establishedwithout the use of the pressure sensor the liquid level sensor. In thisfurther way the vent line 7 may be not ring-closed on the container 2 oron the infusion line 4, but may be connected in another way, for exampleto the line 21 or the atmosphere or to a drainage which is external ofthe infusion device. In this further way, after having filled theemptied container and after having replaced it with a full container ofthe infusion fluid (as in the preceding cases), the infusion pump may beactivated with the vent valve open (the vent valve can be opened before,or during, or after the full container has replaced the emptiedcontainer). The controller in this case can be programmed to pump apredetermined quantity (in weight or volume) of infusion fluid, possiblymixed with air, or to pump at a predetermined velocity for apredetermined time. The quantity in weight can be detected by the weightsensor 3. The quantity in volume can be detected on the base of thecapacity of the positive-displacement pump 5 and the number of operativecycles (rotations) of the pump. The controller is programmed to closethe vent valve 8 and open the infusion block valve 6 after the pumpingaction has ensured appropriate filling of the separator (chamber 9) withliquid. The normal infusion procedure can recommence after a momentarypause of the infusion pump 5, but can restart even without having tostop the infusion pump 5.

Legend

1. Infusion apparatus

2. Batch container of the infusion fluid

3. Weight sensor

4. Infusion line

5. Infusion pump

6. First valve (check or block valve for the infusion fluid)

7. Vent line or excess gas discharge line

8. Second valve or vent valve

9. Infusion fluid expansion chamber (gas-liquid separation chamber)

10. First pressure sensor (pressure sensor downstream of the infusionpump)

11. Second pressure sensor (pressure sensor upstream of the infusionpump)

12. Vent line discharge (infusion line excess gas discharge)

13. Removable connection between the infusion line and the infusionfluid container

14. Blood treatment device having a semipermeable membrane (hemodialyseror hemo(dia)filter or plasma separator or hemoperfusion device ormembrane exchanger)

15. Blood withdrawal line (arterial line)

16. Blood return line (venous line)

17. Blood pump

18. Source of a medical fluid (dialysis fluid source)

19. Fresh medical fluid supply line

20. Drainage

21. Used medical fluid discharge line

22. Removable connection between the vent line and the medical treatmentapparatus

23. Extracorporeal blood circuit

1-38. (canceled)
 39. An infusion apparatus comprising: at least a batchcontainer containing an infusion fluid; an infusion line having a firstend which is connected to the batch container and a second end whichsupplies the infusion fluid; an infusion pump operating on the infusionline for circulation of the infusion fluid from the first end to thesecond end; a first valve designed to close the infusion line betweenthe pump and the second end; a vent line having a first end which isconnected to an intermediate tract of the infusion line and a seconddischarge end, the intermediate tract being arranged between theinfusion pump and the first valve; a second valve designed to close thevent line.
 40. The apparatus of claim 39, comprising a gas-liquidseparator arranged in the intermediate tract.
 41. The apparatus of claim39, comprising: a first sensor for emitting a first signal indicatingthe quantity of liquid in the intermediate tract; control means whichare programmed to receive the first signal and for commanding the firstvalve and/or the second valve on the basis of the first signal received.42. The apparatus of claim 41, wherein the first sensor comprises afirst pressure sensor for emitting a first pressure signal indicating apressure in the intermediate tract.
 43. The apparatus of claim 39,wherein the control means are programmed to perform a first sequence ofstages which comprises: closing the first valve and/or the second valve;activating the infusion pump; and opening the first valve and/or thesecond valve on the basis of the first signal received.
 44. Theapparatus of claim 39, wherein the control means are programmed toperform a second sequence of stages which comprises: closing the firstvalve and the second valve; activating the infusion pump; determining atleast a value of pressure change in the intermediate tract; and openingthe first valve or the second valve on the basis of the pressure changevalue.
 45. The apparatus of claim 44, wherein the second sequence ofstages comprises a stage of selectively opening the first valve or thesecond valve according to whether the pressure change value is greateror, respectively, lower than a reference value.
 46. The apparatus ofclaim 44, wherein the pressure change value in the intermediate tract isdetermined during a predetermined change of another parameter while thepump is activated.
 47. The apparatus of claim 46, wherein the anotherparameter is chosen from a group of parameters comprising the time,volume/weight of fluid displaced by the pump, displacement of a mobileelement of the pump, and a weight of the batch container of the infusionfluid.
 48. The apparatus of claim 46, wherein the pressure change valueis placed in relation with or normalised with respect to the otherparameter.
 49. The apparatus of claim 44, wherein the second sequence ofstages comprises a stage of comparing the pressure change value with areference value, the stage of opening the first valve or the secondvalve being performed as a result of the comparison.
 50. The apparatusof claim 39, wherein the control means are programmed to perform a thirdsequence of stages which comprises: closing the first valve and thesecond valve, activating the infusion pump, determining at least avolume/weight value of the fluid pumped by the infusion pump, comparingthe volume/weight value of the pumped fluid to at least a referencevalue, and opening the first valve or the second valve according to aresult of the comparison.
 51. The apparatus of claim 50, wherein thethird sequence of stages comprises a stage of selectively opening thefirst valve or the second valve according to whether the volume/weightvalue of pumped fluid is lower or, respectively, higher than a referencevalue.
 52. The apparatus of claim 50, wherein the volume/weight value ofthe fluid pumped in the intermediate tract is determined in relation toa predetermined change in another parameter while the pump is in anactivated stage.
 53. The apparatus of claim 52, wherein the otherparameter is chosen from a group of parameters comprising time, pressurechange in the intermediate tract, and volume/weight of the batchcontainer of the infusion fluid.
 54. The apparatus of claim 52, whereinthe value of the volume/weight of pumped fluid is set in relation to ornormalised with respect to the other parameter.
 55. The apparatus ofclaim 50, wherein the third sequence of stages comprises a stage ofcomparing the volume/weight value of the pumped fluid with a referencevalue, the stage of opening the first valve or the second valve beingperformed according to the comparison.
 56. The apparatus of claim 39,wherein the control means are programmed to perform a fourth sequence ofstages which comprises: closing the first valve and the second valve,activating the infusion pump, determining at least a relation between apressure variation in the intermediate tract and a volume/weight offluid pumped by the infusion pump, comparing the value of the relationto at least a reference value, and opening the first valve or the secondvalve according to a result of the comparison.
 57. The apparatus ofclaim 39, wherein the control means are programmed to perform a fifthsequence of stages which comprises: closing the first valve and thesecond valve, activating the infusion pump, acquiring at least apressure valve in the intermediate tract, comparing the pressure valueto at least a reference value, and opening the first valve or the secondvalve according to a result of the comparison.
 58. The apparatus ofclaim 39, wherein the control means are programmed to perform stages asfollow: closing the first valve and the second valve; activating theinfusion pump when the first valve and the second valve are closed;measuring at least a pressure value in the intermediate tract when theinfusion pump is or has been activated; comparing the measured pressurevalue with a threshold value; and opening at least one of the firstvalve and the second valve if the measured pressure value exceeds thethreshold value.
 59. The apparatus of claim 39, wherein the second endof the vent line is connected to an element selected from a group ofelements comprising: the batch container of the infusion fluid, aninitial tract of the infusion line comprised between the batch containerand the infusion pump, a hydrophobic filter connected to the atmosphere,an aspiration device, a fluid transport line connected to a fluidchamber of a blood treatment device having a semi-permeable membranewhich separates the fluid chamber from a blood chamber, and a used fluiddischarge line of a hemo(dia)filtration apparatus.
 60. The apparatus ofclaim 40, wherein the gas-liquid separator comprises an expansionchamber.
 61. The apparatus of claim 40, wherein the first end of thevent line is connected with or engaged to a top of the gas-liquidseparator.
 62. The apparatus of claim 40, wherein the pressure sensor isassociated to the gas-liquid separator.
 63. The apparatus of claim 39,wherein the second end of the infusion line is connected to anextracorporeal blood circuit of an apparatus for extracorporeal bloodtreatment.
 64. The apparatus of claim 39, comprising a weight sensorwhich emits a signal indicating a weight of the batch container, thecontrol means being programmed to perform following stages: opening thefirst valve, closing the second valve, activating the pump with thefirst valve open and the second valve closed, acquiring at least aweight value of the batch container, comparing the weight value with areference weight value, and signalling a faulty situation and/orstopping the pump and/or closing the first valve according to a resultof the comparison.
 65. The apparatus of claim 64, wherein the referenceweight value comprises a weight value of the batch container acquiredpreviously with an aim of assessing whether the weight of the batchcontainer is no longer decreasing, or a predefined value indicating theweight of the empty fluid batch container.
 66. The apparatus of claim39, wherein the control means are programmed to perform a sixth sequenceof stages which comprises: closing the first valve, closing the secondvalve, activating the pump with the first valve closed and the secondvalve closed, acquiring at least a pressure value in the intermediatetract while the pump is or has been activated, acquiring at least avalue of the pressure change in the intermediate tract, and selectivelyopening the first valve or the second valve when the pressure valueexceeds a threshold value, the selection being performed according tothe pressure change value.
 67. The apparatus of claim 39, wherein theinfusion pump is a volumetric pump.
 68. The apparatus of claim 39,wherein the infusion pump is an occlusive pump.
 69. The apparatus ofclaim 39, wherein the pump is predisposed along the infusion linedownstream of the batch container.
 70. The apparatus of claim 39,comprising a second pressure sensor for emitting a second signalindicating the pressure in an initial tract of infusion line comprisedbetween the batch container and the pump.
 71. The apparatus of claim 70,wherein the control means are programmed to perform a seventh sequenceof stages which comprises: acquiring at least a pressure value in theinitial tract supplied by the second pressure sensor, comparing thepressure value in the initial tract with a reference value, andsignalling a faulty situation and/or stopping the pump and/or closingthe first valve according to the comparison.
 72. A method forcontrolling an infusion apparatus comprising stages of: providing aninfusion line having a first end for receiving an infusion fluid and asecond end for supplying the infusion fluid; connecting the infusionline to a pump for circulation of infusion fluid from the first end tothe second end; connecting a first valve to the infusion line betweenthe pump and the second end for closing the line; connecting a first endof a vent line to an intermediate tract of the infusion line arrangedbetween the pump and the first valve, the vent line having a seconddischarge end; connecting a second valve to the vent line for closingthe vent line; providing a first sensor for emitting a first signal ofat least a first parameter indicating a liquid level in the intermediatetract; closing the first valve and/or the second valve; connecting atleast a batch container containing an infusion fluid to the first end ofthe infusion line; activating the pump with the first valve closedand/or the second valve closed; acquiring at least a value of the firstparameter in the intermediate tract following the activation of thepump; comparing the value of the first parameter with a reference value;and opening the first valve or the second valve according to a result ofthe comparison.
 73. The method of claim 72, wherein the first sensorcomprises a pressure sensor.
 74. The method of claim 72, comprisingstages of: determining at least a value of the change of the firstparameter in the intermediate tract during a predetermined change ofanother parameter; comparing the change of the first parameter with areference value; and opening the first valve or the second valveaccording to a result of the comparison.
 75. The method of claim 74,wherein the other parameter is chosen from a group of parameterscomprising time, volume/weight of fluid pumped by the infusion pump,displacement of a mobile element of the infusion pump, and a weight ofthe batch container of the infusion fluid.
 76. The method of claim 72,comprising stages of: a) closing the first valve; b) closing the secondvalve; c) activating the pump with the first valve closed and the secondvalve closed; d) acquiring at least a value of the first parameter inthe intermediate tract while the pump is operating; e) acquiring atleast a value of the change of the first parameter in the intermediatetract; f) selectively opening the first valve or the second valve whenthe value of the first parameter reaches a threshold value, theselection being performed according to the value of the change of thefirst parameter.